1. Field of the Invention
This application relates to energy savings in computer displays and particularly to energy savings in displays of portable computing systems.
2. Background Art
The challenge of managing energy consumption in computer systems such as desktop computers, servers and the like, is finding efficient ways to conserve electricity. In meeting the energy needs of battery-powered computing systems the challenge is to extend battery life beyond a minimal acceptable duration. Battery life is approximated to the relationship between battery capacity and the average power consumed. Ways to increase battery life include increasing the capacity of batteries. Typically, however, increased capacity translates to larger, heavier and more costly batteries. Moreover, rechargeable batteries in mobile computing devices that are not powered by solar cells or self-winding mechanical devices, hold less energy than non-rechargeable batteries. Thus, whichever power source is used, the design of computing systems must still be biased toward energy conservation.
Energy wise, display subsystems are among the largest consumers of any components in computing systems. A display subsystem is broadly defined as any combination of the hardware and software modules associated with the visual representation of data in a computing system, and is hereafter referred to simply as “display”. In particular, each display subsystem includes a display panel (or cathode ray tube—CRT) and in addition it includes a display controller and display drivers corresponding to the display panel technology and an image processing system module. The image processing hardware-software module provides geometry and raster processing. A raster image processor (RIP) is a hardware or combination hardware/software module that converts images described in the form of vector graphics statements into raster graphics images or bitmaps. These modules employ computations to generate each screen. A “screen” is the visual presentation (visible image) fashioned by one or more applications and put on view by a display.
Under normal display usage patterns, battery life in battery-powered devices can be extended with advances in battery technology and low-power circuit designs, including energy efficient displays. However, energy efficiency often comes with less function, or it must be traded off in the design for greater functionality. Thus, without more, such advances may not meet the energy needs of future mobile computing systems with power metrics dominated by normal display usage patterns.
Thus, designs for energy conservation have turned their focus to the patterns of display usage. For instance, devices have been designed with a number of power metrics to decrease the power usage, including power metrics defined by the power consumed in active mode, idle mode, sleep (inactive) mode, and the like. Typically, display usage patterns have been changed by turning the display off or equivalently minimizing the energy usage in the idle and sleep modes.
Another approach proposed reducing the number of pixels to consume less energy. To minimize the number of pixels to be turned on, characters, icons and graphics can be designed with a smaller number of pixels, by reducing font size, etc. However, this approach can impact readability.
To further conserve energy, some approaches have suggested the possibility of zoned backlighting. However, it was believed that design or manufacturing limitations might preclude mass-production of displays that support zoned backlighting.
Another common design involves using smaller displays. However, energy savings with these approaches are limited and invariable once the system is configured. And, no further savings are typically obtained unless the system is reconfigured.
Moreover, these approaches do not take into consideration the varying display real-estate needs of applications and the respective screens-images they fashion. For example, a simple message that indicates “you have mail,” “received call 123.456.7890” or “battery low” does not consume a large piece of display real estate. Yet, if the entire display is turned on when generating such message, higher levels of energy are consumed needlessly. Similarly, simple text-based messages may not need full color and a high refresh rate, and providing full color and a high refresh rate consumes unnecessary energy.
It follows that, even with the foregoing approaches, further improvements directed toward energy conservation are needed. The present invention addresses these and related issues.